[libFuzzer][AFL] Enable fuzzer builds with SanitizerCoverage and without A/M/UbSan.

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 1330a1f8aa3f2d66191b8d3e638eabedfa2197a8..4a0588b0b3c57746c48a72589f2e79b36426936b 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -166,6 +166,10 @@ config("default_sanitizer_ldflags") {
       ldflags += [ "-fsanitize=vptr" ]
     }
 
+    if (use_sanitizer_coverage) {
+      ldflags += [ "-fsanitize-coverage=$sanitizer_coverage_flags" ]
+    }
+
     if (is_cfi && !is_nacl) {
       ldflags += [ "-fsanitize=cfi-vcall" ]
       if (use_cfi_cast) {